In optical transmission systems optical signals are transmitted over an optical fiber. If the fiber is accidentally cut or disconnected and the optical signal would still be transmitted a service person would be harmed, if he happened to look at the concentrated light signal being emitted from the broken fiber. To avoid such harm, there is the need for a safety arrangement that automatically reduces the power of a light signal to avoid injuries. High optical power at the open fiber end must be also avoided before fiber resplicing or patchcord reconnecting.
The U.S. Pat. No. 6,359,708 B1 describes a facility which detects the loss of a high power optical signal in an optical transmission path and invokes a procedure which causes a transmitter connected to the cut fiber to reduce the power level of an optical signal emitted to a safe power level.
The same procedure may be applied to a multi stage amplifier if a connection between the stages is interrupted.
And the same safety arrangement is also necessary within an optical apparatus comprising a plurality of circuit packs (optical devices), which are connected via optical fibers. A possibility to avoid high optical power inserted into a broken fiber is to interrupt the line directly downstream of a transmitter/optical amplifier, or to shut down the transmitter/optical amplifier, or to strongly reduce the output power, if a LOS (loss-of-signal) is determined, or equivalently a “signal-present” of the signal, confirming a faultless connection, cannot be determined. If the fiber system is closed again, it is desirable that the signal-present signal is automatically detected and original power level is recovered. But especially in systems where the optical signal is split and sent to a plurality of circuit packs the strong reduction of power level of the transmitter results in interrupting or at least impairing all other connections.
Another possibility is to avoid an interruption and to control the power of the transmitter up to a predetermined safe value. Thereby the emitted power at the broken end further down the fiber is reduced to the safe power value or even below, and the power sent to other circuit packs may be far below a sufficient value required for signal transmission.
Therefore, in many cases, especially when a plurality of channels is transmitted, this method leads to not necessary impairments.